A digital television (DTV) signal represents a combination of multiple streams of data packets, i.e., it is a packet multiplex. A DTV signal that is compliant with the American Television Standards Committee (ATSC) standard for digital terrestrial television has a packet multiplex that can be depicted as in FIG. 1. Such a DTV packet multiplex is complex. Each data packet in the multiplex contains 188 bytes, a 4-byte header and a 184-byte payload. The packet header contains a 13-bit “packet id” field (PID) that is used to tell what stream the packet belongs to.
A DTV system can include the transmission subsystem and the reception subsystem. Problems with such a DTV system can arise in either subsystem. Engineers and technicians working with a DTV system need a monitoring/diagnostic instrument that meets the specific needs of their circumstances. Some of the tasks performed by such engineers and technicians are included in the following list:
Task 1: Installation and maintenance of digital television broadcast equipment, especially the digital components.
Task 2: Miscellaneous monitoring and troubleshooting tasks for a digital television broadcaster, including informal testing of the station's geographical area of coverage.
Task 3: Continuous monitoring of a digital television broadcast at the broadcast station.
Task 4: Installation and maintenance of high end digital television reception equipment, such as for a home theatre system or a relay station.
To troubleshoot the problems, or merely monitor one or both of the subsystems, of a DTV system, the following general classes of functions can be especially useful.
Function 1: Playing of broadcast digital television audio and video in real time. This allows the user (of the functionality) to check quickly and easily what broadcast signals are actually on the air, whether both audio and video components of the desired programs are present, and whether the data formats are correct (so that a receiver can play them without error). This also gives an immediate indication of whether the signal has “lip sync” problems—situations where the audio and video components of a program are not synchronized correctly, so that lip movements and the corresponding sounds come at slightly different times.
Function 2: Play digital television audio and video from a recorded broadcast stream. This allows a user to check whether audio and video components are present, correctly formatted, and correctly synchronized in a recorded broadcast stream. And it allows problems to be rechecked at a later time and/or to be communicated to someone else who could not observe them in real time.
Function 3: Take digital television input from an antenna, and monitor the quality of the incoming signal. This allows the user to receive the broadcast when there is no convenient signal source other than an antenna, and to tell whether problems receiving a broadcast through an antenna are due to a weak or distorted signal, or due to errors in the format of the digital data. It also helps the user to aim the antenna properly.
Function 4: Record the digital transport stream. This allows the user to capture data for later lab analysis of particularly troublesome problems.
Function 5: Monitor digital properties of a broadcast signal on-line, i.e., as it is being broadcast. This allows the user to detect various kinds of problems automatically as they occur, enabling rapid correction.
Function 6: Analyze digital properties of a broadcast signal off-line, from a recording. This allows the user to drill down into detailed digital properties of a broadcast stream in more detail than might be possible with on-line monitoring alone.
As to Function 3, to monitor the quality of an incoming DTV signal using ATSC vestigial side band (VSB) modulation on-line, i.e., as it is being broadcast, any or all of the following functions can be especially useful.
Function 3.01: Monitor packet error rate for decoding the VSB segments into MPEG-2 packets.
Function 3.02: Monitor signal-to-noise ratio after equalization and phase correction, at the point where the signal goes into the VSB decoder.
Function 3.03: Display snapshots of the tap coefficients and total tap energy from the equalization stage.
Further as to Function 5, to monitor digital properties of an incoming ATSC DTV signal packet multiplex on-line, i.e., as it is being broadcast, any or all of the following functions can be especially useful.
Function 5.01: Analyze the syntax of MPEG-2 transport packets.
Function 5.02: Analyze existence, syntax, consistency, and frequency of MPEG-2 System tables and ATSC PSIP tables.
Function 5.03: Analyze percentage of the transport stream used by various data types, channels, and elementary streams.
Function 5.04: Analyze accuracy, jitter, and transmission frequency of the Program Clock References (PCRs).
Function 5.05: Generate alarms on errors and exceeding specified thresholds.
Function 5.06: Trigger a recording on errors and exceeding specified thresholds.
As to Function 6, off-line analysis of an ATSC broadcast stream includes, but is not limited to, any or all of the Functions 5.01-5.10 and/or any or all of:
Function 6.1: Drill down into the contents of individual MPEG-2 transport packets.
Function 6.2 Present a visualization of the individual MPEG-2 transport packets in the broadcast stream.
Someone who wishes to troubleshoot and/or monitor a DTV signal will desire a monitoring/diagnostic tool that affords maximum convenience and can be obtained at minimum manufacturing cost (and therefore minimum sales price). To achieve such goals, the functions needed for a user's application should be packaged/integrated in an easily portable chassis. This is especially important for field testing, where the instrument may need to be carried on an airplane and in the back of a rental car.
It is a problem that most existing digital television monitoring/diagnostic equipment is oriented toward the lab testing (as opposed to field testing) environment and, moreover, does not contain the right mix of functionalities discussed above, especially not integrated within an easily portable chassis.